The present invention relates generally to the field of controlling the growth of plants in splits found in cement or asphalt pavements. The invention, more particularly, relates to the field of long-term control of plant growth in the splits.
Pavements are usually made of asphalt and concrete but can also be constructed by a variety of building materials such as stone, brick and cobblestone. Such pavement structures including sidewalks and curbs are usually engineered with seams and/or expansion joints. The expansion joints are intended to function to either prevent or limit the formation of cracks in the pavement caused by thermal/pressure excursions such as those caused by weather.
Most commonly, cracks are caused by natural processes such as freezing and thawing of the pavement caused by weather conditions. Because of the freezing and thawing, the integrity of the joints in the pavement may be reduced or worse, cracks may form in the pavements. Further, enlargement of both the manufactured or naturally created splits can occur during severe cold weather when water infiltrates into the splits. As used in this specification and the appended claims the term "split" is defined to mean any type of divide in the pavement including cracks, joints and seams.
The problem associated with splits in the pavement can be amplified by plants. The joints, the seams and the cracks in the pavement serve as natural collection points for wind dispersed plant seeds. Moisture and soil which accumulate in the cracks provide an ideal environment for plants allowing the seeds to sprout. Upon germinating, the plants accentuate the problem of crack enlargement by further inducing the cracks. Moreover, roots of plants in the soil below pavement can grow into plants through the splits in the pavement.
In addition to enlarging the splits, the plants growing in the splits can also cause litter problems because they are capable of trapping litter, such as, paper wrappers as they are being blown about by the wind. This problem is especially troublesome on aircraft runways, tax-ways and aprons. Such plant growth may obscure the view of airport runway lights endangering the lives of airplane passengers. Moreover, the litter which accumulates in the runways due to the growth of plants in pavement splits can even be sucked into jet engine or into reciprocating engine intakes, to cause damage or malfunction of engines.
To alleviate the plant problem, a quick temporary solution is provided by mowing. A more permanent method has been developed which requires the splits to be routed and then sealed with either asphalt or butyl sealants. In the most severe cases, repaving the runway, taxi-way or apron may be required.
Although routing and sealing is effective for removing plants that have grown in the splits at the time the pavement is either routed and sealed or repaved, the method is not a solution for the long-term control of the plant problem in splits. That is, if the splits have been routed and sealed, the seal will eventually deteriorate thereby reopening the splits. Once the splits are reopened, the growth of plants in the reopened splits presents the same problems as those discussed above. Therefore, routing and sealing the splits does not alleviate the problem of plant growth in splits (including cracks, joints or seams). It continues to be a recurring problem.
It is known in the art that plant seedlings may be controlled by the use of pre-emergence herbicides. For example, Soper, U.S. Pat. No. 3,257,190, Soper, U.S. Pat. No. 3,111,403, Lignowski and Scott, Trifluralin and Root Growth, 12 Plant & Cell Physiology 701 (1971), and Eshel and Katan, Effect of Dinitroanilines on Solanaceous Vegetables and Soil Fungi, 20 Weed Science 243 (1972), all teach the use of 2,6-dinitroaniline as a herbicide which eliminates germinating seedlings. Furthermore, Koestler, U.S. Pat. No. 4,360,376 teaches incorporating 2,6-dinitroaniline into a microcapsule capable of releasing it. Although these references teach the use of pre-emergence herbicides to control the growth of plants, they do not provide a practical solution which may be used in long-term control of plant growth in pavement splits, including joints, cracks or seams.
By applying a herbicide in a single application to a split (a crack, joint or seam) in the pavement, the initial concentration of herbicide is much greater than needed. However, the concentration becomes too low to be a truly effective retardant with the passage of time. The concentration of herbicide in the applied area is lowered because of physical, chemical and even biological activity.
Therefore, it is desirable to provide a method and device in which the herbicide can be metered out in the split at a preselected rate. Additionally, it is desirable to provide a method and device which protects the herbicide from degradation and physical loss from the split.
Another problem with using pre-emergence herbicides, such as 2,6-dinitroaniline is that such herbicides do not eliminate existing plants. In other words, the growth of perennial plants from existing roots is largely unaffected by presence of a pre-emergence herbicide in the split.
A problem with prior art controlled release devices such as those disclosed in U.S. Pat. No. 3,864,114 (Green) is that the operation of the device disclosed in that patent is based on leaching the herbicide. Water penetrates the device and leaches out the herbicide. Generally, water degrades the herbicide in a relatively short period of time of about 2 to 6 weeks.
In light of the problem encountered by the growth of plants in pavement cracks, joints, and seams, there presently exists a need for a method and/or device which prevents such growth for extended periods of time. Such an arrangement would help minimize the amount of destruction and danger caused by plant growth in highways, airport runways, sidewalks and generally in any type of use of concrete and asphalt.
Thus, one object of the present invention is to provide a product and a method for controlling, for a prolonged period of time (2 to 10 years) the growth of plants in splits by preventing seeds from germinating and also by preventing the growth of plants from existing roots.
Another object of the present invention is to provide a controlled-release device and a method in which the release of the herbicide is driven by temperature.
A further object of the present invention is to provide a controlled release device and method in which the release rate of the herbicide and its effectiveness can be predetermined.
A still another object of the present invention is to provide a controlled release device and method in which the herbicide is protected from chemical and biological degradation prior to being released from the device.
A yet further object of the present invention is to provide environmentally superior controlled release herbicide device and method in which the herbicide is localized and does not spread far into the soil surrounding the system.
A still further object of the present invention is to provide herbicidal device which can be easily inserted into the splits and which is retained in the splits for a prolonged period of time.
Other objects of the present invention will become apparent to those skilled in the art upon studying this disclosure.